I've mentioned this before somewhere on here but I'm not a fan of using real formula.
If I make any it's basically a DIY version of "soylent", the meal replacement drink that you can buy, Soylent is really expensive but you can buy a number of powders (proteins, vitamins etc.) that can be measured and mixed into a drink that you can live on and still get you entire daily dietary requirements. There is a site with recipes for how to make your own and depending on how you make it and how much you buy at a time can get the price down to about £3.50 (maybe $5) for a whole days worth of liquid "meals".
There are people out there who live perfectly healthy on nothing but their soylent but I couldn't do that I like food too much.
At the moment though I have been using Ensure Nutrivgor, it's a powdered shake that is recommended and often given by doctors to people who are unable to eat solid food for medical reasons, it also has everything you need to live on and comes in a few flavours (i get strawberry) but can also be quite costly to use all the time.
I can't eat breakfast when I wake in the morning until a good hour after getting up by which time I'm at work so I have one of these shakes for breakfast and it does the job nicely.